Process for electroforming microparts having hollow interiors

ABSTRACT

An electroforming process for manufacturing microparts comprises forming a mold cavity having the configuration of the desired micropart in a resin plate, lining the interior of the mold cavity with an electrically conductive material, attaching a lead wire to the electrically conductive material, immersing the mold cavity in an electrolytic bath, supplying dc electric energy to the lead wire to electrodeposit a metal layer of substantially uniform thickness and which comprises the micropart within the mold cavity, removing the electroformed micropart from the mold cavity, and finally removing excess portions of the electrodeposited material to obtain a finished micropart. To ensure uniform thickness of the electrodeposited material, the ratio of the height of the side wall to the width of the bottom wall of the mold cavity is preferably maintained at a value less than 3:1.

United States Patent [191 Shimada et al.

PROCESS FOR ELECTROFORMING MICROPARTS HAVING HOLLOW INTERIORS [73] Assignee: Kabushiki Kaisha Daini Seikosha,

Tokyo, Japan [22] Filed: June 15, 1972 [21] Appl. No.: 263,094

[30] Foreign Application Priority Data June 15, 1971 Japan 46-42689 52 us. c1. 204/4, 204/9 [51] Int. Cl. C23b 7/00, C23b 7/02 [58] Field of Search 204/3, 4, 6, 9

[56] References Cited UNITED STATES PATENTS 1,206,881 12/1916 Miller 204/4 1,570,634 1/1926 Laukel 204/4 2,335,774 11/1943 Landry 204/4 2,841,548 7/1958 Perlman.... 204/4 3,441,487 4/1969 Rea et al 204/4 OTHER PUBLICATIONS Modern Electroplating, 2nd Edition, (1963), Fred Dec. 10, 1974 Lowenheim, John Wiley & Sons, Inc., pgs. 272, 273, 282, 283, 285, 286.

Primary ExaminerT. M. Tufariello Attorney, Agent, or FirmRobert E. Burns; Emmanuel J. Lobato; Bruce L. Adams [57] ABSTRACT An electroforming process for manufacturing microparts comprises forming a mold cavity having the configuration of the desired micropart in a resin plate, lining the interior of the mold cavity with an electrically conductive material, attaching a lead wire to the electrically conductive material, immersing the mold cavity in an electrolytic bath, supplying dc electric energy to the lead wire to electrodeposit a metal layer of substantially uniform thickness and which comprises the micropart within the mold cavity, removing the electroformed micropart from the mold cavity, and finally removing excess portions of the electrodeposited material to obtain a finished micropart. To ensure uniform thickness of the electrodeposited material, the ratio of the height of the side wall to the width of the bottom wall of the mold cavity is preferably maintained at a value less than 3:1.

10 Claims, 13 Drawing Figures PATENT}; SEC 1 01914 sum 10F DIM. RATIO 3=l DIM. RATIO 2=| FIG. IB

Dimension Ratio Dimension Ro'tio 2=| Dimension Ratio 3 i O 0 i O O my 6 5 4 3 2 A z. zoEmonGQoEQwd mo 9.5m

mmmzxoik Current Density in /dm Duration of Electroforming in hou VII/I111; F/G. 4B

PATENTEB DEC] 01974 SHEET 2 OF 2 FIG. 55

FIG. 6A

FIG. 8

PROCESS FOR ELECTROFORMING MICROPARTS HAVING HOLLOW INTERIORS Most of the conventional manufacturing processes for forming microparts for watch escapement mechanisms comprise pressing operations wherein the parts are pressed from plates of brass, nickel-silver, or steel and the pressed parts are then suitably finished by either cutting or grinding. Another manufacturing process more recently employed in the industry has been electroforming wherein the desired watch part is formed by electroplating.

The manufacturing of watch microparts by pressing is disadvantageous since the pressed parts have too heavy a weight and consequently their inertia is too great to permit them to move rapidly back and forth. One attempt to solve this problem has been to press the parts from aluminum alloy sheet which has a comparatively light weight. This attempt has been unsatifactory when applied to pallet forks of escapement mechanisms since the guard pin of the pallet fork repeatedly collides with the roller jewel of the balance wheel during operation of the escapement mechanism and since the guard pin was formed of aluminum, it became easily worn and hence aluminum pallet forks are not feasible for practical use.

The manufacturing of watch microparts by electroforming has heretofore also been disadvantageous since pallet forks made by such a process typically have a weight at least equal to and oftentimes greater then pallet forks formed by pressing. Moreover, the dimensional accurracy of electroformed watch parts has not been too uniform and therefore internal stresses are usually present in the watch parts which frequently causes them to warp or otherwise distort themselves from their intended configuration. One of the advantages of the electroforming technique is that the watch parts have substantially the same strength and wearability as those parts formed by the more conventional pressing techniques.

One attempt to overcome the disadvantageous heavy weight of the electroformed watch parts has been to form a deep groove in the watch part during the electrodeposition process. Unfortunately, the watch parts heretofore made by this tecnique are not suitable for actual use since they lack the necessary mechanical strength and usually the thickness of the corner portions of the watch part is only one tenth that of the remaining portion. The reason for this is that the metallic ions in the electrolytic solution have difficultyreaching the corners of the watch part and hence electrodeposition at the corners is carried out to a lesser extent than at the remaining portions of the watch part.

It is therefore a primary object of the present invention to provide a process of electroforming microparts which have a substantially hollow interior to lessen the weight of the part yet have sufficient strength and mechanical wearability to render them suitable for commercial use.

Another object of the present invention is to provide a process of electroforming microparts which may be commercially carried out on a mass production basis.

A further object of the present invention is to provide a process of electroforming microparts wherein the amount of electrodeposition which does not actually constitute part of the final product is held to a minimum thereby increasing the efficiency of electrodeposition.

A still further object of the present invention is to provide a process of electroforming microparts which are substantially free of internal warping caused by compressive and tensile stresses developed during the electroforming process.

The foregoing objects and other objects of the present invention are accomplished by forming a mold cavity having the shape of the desired microparts in a resin plate, lining the mold cavity with an electrically conductive lining, attaching a lead wire to the electrically conductive lining, immersing the mold cavity into an FIG. 2 is a graph showing the relationship between the thickness ratio of electrodeposition vs. both current density and the duration of electroforming;

FIG. 3 is a perspective view showing the directions of electrodeposition growth;

FIG. 4A is a plan view of a mold cavity used in the process of the present invention for electroforming a pallet fork and FIG. 4B is a cross-sectional view taken aiong the line 4B-4B in FIG. 4A;

FIG. 5A is a plan view of a pallet fork made by the electro-forming process of the present invention and FIG. 5B is a cross-sectional view taken along the line 5B--5B in FIG. 5A;

FIG. 6A is a plan view of a plurality of mold cavities used for electroforming pallet forks in accordance with the present invention and FIG. 6B is a cross-sectional view taken along line 68-63 in FIG. 6A;

FIG. 7 is an explanatory view of one technique for attaching lead wires to the mold cavities; and

FIG. 8 is a plan view of a portion of an escape wheel madein accordance with the electroforming process of the present invention.

The principles of the present invention will first be discussed in conjunction with FIGS. 1 and 2. FIGS. 1A, 1B and 1C are cross-sectional views showing various molds containing electroformed products for three different size products.

The mold comprises a resin plate 1 having a mold cavity 2 formed therein having steep side walls termi nating at their base in a bottom wall and having the shape and configuration of the desired part or article. The mold cavity 2 is formed by casting a metal block into the configuration of the desired part and then heating the metal casting and transferring same to the resin plate while in a hot state to impress in the resin plate a mold cavity having a shape complementary to that of the metal casting. In other words, the metal casting comprises a male member and forms in the resin plate a female member which exactly complements the male member.

FIG. IA shows a mold cavity 2 having a dimension ratio h/d equal to the height of depth h of the cavity relative to the width (1' of the cavity of l:l. FIGS. 18 and 1C show dimension ratios of 2:1 and 3:1, respectively.

After the mold cavity 2 is imprinted in the resin plate, the entire inner surface of the mold cavity is coated with a layer 4 of silver or some other electrically conductive material and this layer subsequently functions as a cathodic electrode during the electroforming process. A lead wire 3 is attached to the base of the resin plate in electrical contact with the layer 4 and. thus the mold cavity is lined with an electrically conductive layer which may be connected through the lead wire 3 to a source of electric power.

The mold is then immersed in an appropriate electrolytic solution which contains dissolved salts of the metal to be deposited. The lead wire 3 is connected to the negative terminal of a dc voltage source thereby making the electrode 4 a cathode and a metal to be deposited onto the metallic layer 4 is inserted into the electrolytic solution and connected to the positive terminal of the dc voltage source and made the anode. Since the anode and cathode are connected to respective terminals of the dc voltage source, metallic ions begin to migrate and deposit upon the cathode to electroform a hollow micropart 9 having an outer configuration corresponding to that of the mold cavity 2.

Several experiments were conducted in accordance with the present invention and the results of these experiments are graphically shown in FIG. 2. The experiment comprised electroforming three different size parts having dimension ratios of l:l. 2:l and 3:1 such as shown in FIG. 1. The composition of the electrolytic solution was:

Nickel sulphamate 250 g/litre Boronic acid 30 g/litre Nickel chloride g/litre Sodium dodecyl sulfonute 2.5 g/litre Sodium l.3.b-naphthalene-trisuffonate 2.5 g/litre and the appropriate electroforming parameters were:

temperature of solution 48C current density (Aldm l L5 2. 3. 4. 5 time of clectroforming (hrs) 6.7, 5. 3.3. 2.5. 2

of the electrodeposited material on one side portion of the mold cavity 2. As can be seen from examining FIG. 2, the thickness ratio of the electrodeposited material decreases both with increasing current densities and increasing durations of electroforming.

When the current density is 5A/dm the electrode position near the top opening of the mold cavity increases while the quantity of material deposited on the side walls and bottom of the mold cavity remains quite thin. As may he clearly seen from examining FIG. 2, the thickness ratio of electrodeposition decreases with an increase in the dimension ratio and this is primarily because it is more difficult for the metallic ions in the electrolytic bath to move into the mold cavity as the cavity becomes thinner. In addition, as the mold cavity becomes thinner, greater amounts of excess material 9a is deposited and accummulated near the opening of the mold cavity thereby reducing the size of the opening and further hindering the influx of metallic ions to the remainder of the mold cavity. Thus, in order to obtain a uniform thickness of the electroformed parts, the current density should preferably be less than SA/dm when the dimension ratio is less than 1:1 and less than 4A,!dm when the dimension ratio is 2:].

Upon completion of the electroforming operation, the resulting electroformed part 9 is removed from the mold cavity and is appropriately finished to obtain a workpiece having uniform thickness. As seen in FIGS. 1AlC, the part 9 is cut along the chain line to remove the useless excess portion 9a and then the part is ground or otherwise machined to uniformize the thickness of the part.

As seen in FIGS. lA-lC, the entire thickness of each part 9 except for the portions 9a is substantially uniform. Since the entire inner surface of the mold cavity 2 is lined with an electrically conductive material. the electrodeposited material accummulates and grows upon the lining simultaneously in three directions such as shown by the arrows in FIG. 3. Since the electrode posited material is simultaneously deposited in three directions, internal stresses in the workpieces are greatly reduced since the stresses complement and offset one another and cancel each other out. (Somequently, the workpieces formed according to the process of the present invention have a long useful life since they do not have areas of localized stress.

Referring now to FIGS. 4 7, the process of the pres ent invention will be described in conjunction with the forming of a pallet fork for a watch escapement mechanism. First a metal casting is made having the configuration of the pallet fork and the dimension ratio of the height of the pallet fork relative to its width in any cross-section thereof is preferably less than 3:1. The metal casting is then heated and impressed upon the surface of a resin plate I as shown in FIG. 4A to form in the resin plate a mold cavity 2 having the configuration of the pallet fork. The resin plate is composed of thermal plastic resin such as vinylchloride resin, so called A, B, C resin, acrylic resin, polyvinyle acetate resin, polyethylene resin, polypropylene resin, etc.

When the metal casting is transferred to the resin plate, a lead wire 3 is embedded in the resin plate beneath the mold cavity and exposed to the bottom of the mold cavity. Then a thin electric conductor is disposed around the entire interior of the mold cavity and in this example, the electric conductor comprises a silver coating. As seen in FIG. 4A, the conductor 4 completely covers the exposed surfaces of the mold cavity and is in electrical contact with the lead wire 3. Those portions of the electric conductor 4 which extend away from the mold cavity opening are then removed by grinding or another suitable method in order to prevent the formation of excessively deposited material adjacent the mold cavity which would hinder the electroformation of a uniform part.

FIGS. 5A and 5B are respectively plan views and longitudinal cross-sectional views of a pallet fork made by the process of the present invention. As clearly seen in the Figures, the pallet fork 5 is provided with a substantially hollow interior 6 which greatly reduces the mass of the pallet fork and the pallet fork has a substantially uniform wall thickness and therefore does not have areas of localized stress which would decrease the strength of the pallet fork.

In accordance with another aspect of the present invention, a plurality ofmicroparts may be electroformed at the same time. Considering again the case where pal-' let forks are to be made, FIG. 6A discloses a type of resin plate 1' having thereon a plurality of mold cavities 2' each ofwhich is similar to the individual mold cavity 2 disclosed in FIG. 4A. The mold cavities 2' are alternately inverted in order to minimize the space required and in this embodiment, the lead wire is formed by depositing a strip of electrically conductive material into a channel or groove formed in the resin plate 1' interconnecting the various mold cavities 2'. The channel is formed in a manner similar to the formation of the mold cavities 2' and then the channel is lined with a film of silver or other appropriate electrically conductive material. Alternatively, the plurality of mold cavities and the interconnecting channel may be simultaneously formed with a single metal casting.

Another technique for attaching the lead wires to the mold cavities is shown in FIG. 7. A resinplate 1' has a plurality of mold cavities 2' formed therein each of which has a configuration of the desired pallet fork. For the sake of simplicity and clarity, the individual mold cavities 2' have been shown as circules rather than the more intricate pallet-shape. A screen 10 is then superposed over the resin plate 1 and the screen 10 contains therein a plurality of slots 10a which are each located to overlie and interconnect one row of mold cavitiesZ' when the screen is superposed over the resin plate 1'. Then. an electrically conductive material is vacuumdeposited through the slots 10a by vacuum-evaporation whereby the individual mold cavities 2' are electrically connected by thin electric leads or conductors 3'. After the pallet forks are formed by electroforming, the unnecessary remaining portions of the electric conductors 3' are ground away.

A plurality of resin plates 1', such as shown in FIG. 6A, were constructed and immersed into an electrolytic bath and the various lead wires connected in parallel to an electric voltage source and a plurality of pallet forks were produced in accordance with the aforementioned process. The composition of the electrolytic bath was:

Nickel sulphamate 250 g/litre Boronic acid 30 g/litre Nickel chroride 5 g/litre Sodium dodecyl sulfonate 2.5 g/litre Sodium l.3.6-naphthalene-trisuffonate 2.5 g/litre The Parameters of clectroforming were:

-Continued temperature of solution 45-50C. current density 2A/dm time of electrodeposition 5 hrs.

The average thickness of various portions of the pallet forks produced in accordance with the aforementioned process are shown in the following Table for the dimension ratios 1:], 2:1, and 3:1.

Upon completion of the electroforming operation, the individual pallet forks were removed from the resin plates and the electroformed pallet forks were then finished by cutting off the useless upper portions 9a and then the pallet forks were ground into a uniform thickness. The resulting pallet forks 5 had the configuration shown in FIGS. 5A and 5B.

The pallet forks constructed in accordance with the process of the present invention have commercially acceptable mechanical strength yet have a light weight due to the hollow interior 6 and compare quite favorably with pallet forks formed by the conventional pressing technique. During use of the pallet fork in an escapement mechanism, the arcuate tip. portion 5a cooperates with a pallet jewel and the mechanical strength of the part 50 compares with the mechanical strength of corresponding parts of conventional pallet forks as follows:

Nickel-silver pallet fork 225g Steel pallet fork 532g Electroformed pallet fork .342g

Thus it may be seen that the steel pallet fork has the greatest strength and the electroformed pallet fork constructed in accordance with the process of the present invention has a lower strength than the steel pallet fork but is much superior in strength than the nickel-silver pallet fork. As a practical matter, the electroformed pallet fork has sufficient strength to enable its use in watches.

The process of the present invention is applicable for other components as well as pallet forks and FIG. 8 discloses a portion of an electroformed escape wheel manufactured in accordance with the present invention. As seen in FIG. 8, the escape wheel 8 has a hollow interior 7 and is formed by first constructing ametal casting having the configuration of the escape wheel and then the metal casting is transferred while in a hot state to a resin plate to form a mold cavity in the resin plate corresponding to the shape of the metal casting. Then a thin electric conductor is formed on the interior surface of the mold cavity and then the escape wheel is electroformed in a manner similar to that used in electroforming the pallet forks.

Through the process of the invention has been described in' conjunction with the formation of watch parts, the process of the invention is not limited to the formation of watch parts and is applicable to the form ation of any other microparts. Moreover, though the electrolytic solution has been described as comprising a nickel-bath, it is understood that other metal baths may be used depending upon the desired composition of the electroformed article.

While a preferred embodiment of the invention has been shown and described in detail, it is understood that many modifications and changes will be readily apparent to those skilled in the art and the present invention includes all such obvious modifications and changes falling within the spirit and scope of the invention as defined in the appended claims.

What l claim is:

l. A process for electroforming articles such as watch pallet forks and the like having hollow deep-bottomed interiors comprising: forming in a plate of electrically nonconductive material a plurality of mold cavities each having steep side walls terminating at their base in a bottom wall and having a depth to width ratio no greater than 3:] and having a configuration complementary to that of the exterior of an article to be formed; lining each said mold cavity with a layer of electrically conductive material while leaving the intervening spaces which remain on the plate between the cavities free of electrically conductive material; electrically connecting together each layer of electrically conductive material with a common lead wire which comprises a first electrode; then immersing the plate in an electrolytic solution containing dissolved salts of the metal to be deposited; placing a second electrode in said electrolytic solution; and applying dc electrical energy to said first and second electrodes to obtain a current density less than SA/dm for a time period sufficient to effect substantially uniform electrodeposition of metallic ions from within said electrolytic solution onto each said layer of electrically conductive material to electroforrn thereon a hollow article having steep side walls terminating at their base in a bottom wall and having a substantially hollow interior and an external configuration complementary to that of its corresponding mold cavity.

2. A process according to claim 1; wherein said forming step comprises producing a plurality of metal castings each having a configuration similar to that of one article to be formed, and impressing said metal castings while in a heated state onto said plate to form therein said mold cavities.

3. A process according to claim 1 wherein said forming step includes forming a plurality of mold cavities each having a depth to width ratio of 2:1; and wherein said applying step includes applying sufficient dc electrical energy to said first and second electrodes to obtain a current density no greater than 4 A/dm 4. A process according to claim 1 including attaching said common lead wire to said plate and exposed to the interior of each said mold cavity during the formation of said mold cavities.

5. A process according to claim 1 wherein said im mersing step comprises immersing said plate in an electrolytic solution composed of Nickel sulphamate 250 g/litre Boronic acid 30 g/litre Nickel chroride 5 gilitre Sodium dodecyl-sulfonate 2.5 g/litre Sodium Lib-naphthalene trisuffonate 2.5 g/litre and maintained at a temperature of from 45 to 50 C.

6. A process according to claim 1; including simultaneously using a plurality of plates each containing therein a plurality of mold cavities.

7. A process according to claim I; wherein said electrically connecting together step comprises superposing a cover member having a plurality of slots therein over said plate so that said slots collectively overlie and interconnect all of said mold cavities. and depositing on said plate through said slots an electrically conductive material comprising said common lead wire.

8 A process according to claim 7; wherein said depositing step comprises vacuum-evaporating said electrically conductive material onto said plate.

9. A process according to claim 1; including attaching said common lead wire to said plate such that said lead wire extends along each mold cavity bottom wall and is exposed to the interior of said mold cavity; and wherein said lining step comprises lining each mold cavity and the exposed portion of said lead wire with a layer of electrically conductive material.

10. A process according to claim 1; wherein said applying step is carried out while said lined plate is immersed directly in said electrolytic solution without containing thereon any additional means for directing and guiding the metallic ions into said mold cavities. 

1. A PROCESS FOR ELECTROFORMING ARTICLES SUCH AS WATCH PALLET FORKS AND THE LIKE HAVING HOLLOW DEEP-BOTTOMED INTERIORS COMPRISING: FORMING IN A PLATE OF ELECTRICALLY NONCONDUCTIVE MATERIAL A PLURALITY OF MOLD CAVITIES EACH HAVING STEEP SIDE WALLS TERMINATING AT THEIR BASE IN A BOTTOM WALL AND HAVING A DEPTH TO WIDTH RATIO NO GREATER THAN 3:1 AND HAVING A CONFIGURATIONN COMPLEMENTARY TO THAT OF THE EXTERIOR OF AN ARTICLES TO BE FORMED; LINING EACH SAID MOLD CAVITY WITH A LAYER OF ELECTRICALLY CONDUCTIVVE MATERIAL WHILE LEAVING THE INTERVENING SPACES WHICH REMAIN ON THE PLATE BETWEEN THE CAVITIES FREE OF ELECTRICALLY CONDUCTIVE MATERIAL; ELECTRICALLY CONNECTING TOGETHER EACH LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL WITH A COMMON LEAD WIRE WHICH COMPRISES A FIRST ELECTRODE; THEN IMMERSING THE PLATE IN AN ELECTROLYTIC SOLUTION CONTAINING DISSOLVED SALTS OF THE METAL TO BE DEPOSITED; PLACING A SECOND ELECTRODE IN SAID ELECTROLYTIC SOLUTION; AND APPLYING DC ELECTRICAL ENERGY TO SAID FIRST AND SECOND ELECTRODES TO OBTAIN A CURRENT DENSITY LESS THAN 5A/DM2 FOR A TIME PERIOD SUFFICIENT TO EFFECT SUBSTANTIALLY UNIFORM ELECTRODEPOSITION OF METALLIC IONS FROM WITHIN SAID ELECTROLYTIC SOLUTION ONTO EACH SAID LAYER OF ELECTRICALLY CONDUCTIVE MATERIAL TO ELECTROFORM THEREOF A HOLLOW ARTICLE HAVING STEEP SIDE WALLS TERMINATING AT THEIR BASE IN A BOTTOM WALL AND HAVING A SUBSTANTIALLY HOLLOW INTERIOR AND AN EXTERNAL CONFIGURATION COMPLEMENTARY TO THAT OF ITS CORRESPONDING MOLD CAVITY.
 2. A process according to claim 1; wherein said forming step compriSes producing a plurality of metal castings each having a configuration similar to that of one article to be formed, and impressing said metal castings while in a heated state onto said plate to form therein said mold cavities.
 3. A process according to claim 1 wherein said forming step includes forming a plurality of mold cavities each having a depth to width ratio of 2:1; and wherein said applying step includes applying sufficient dc electrical energy to said first and second electrodes to obtain a current density no greater than 4 A/dm2.
 4. A process according to claim 1 including attaching said common lead wire to said plate and exposed to the interior of each said mold cavity during the formation of said mold cavities.
 5. A process according to claim 1 wherein said immersing step comprises immersing said plate in an electrolytic solution composed of
 6. A process according to claim 1; including simultaneously using a plurality of plates each containing therein a plurality of mold cavities.
 7. A process according to claim 1; wherein said electrically connecting together step comprises superposing a cover member having a plurality of slots therein over said plate so that said slots collectively overlie and interconnect all of said mold cavities, and depositing on said plate through said slots an electrically conductive material comprising said common lead wire.
 8. A process according to claim 7; wherein said depositing step comprises vacuum-evaporating said electrically conductive material onto said plate.
 9. A process according to claim 1; including attaching said common lead wire to said plate such that said lead wire extends along each mold cavity bottom wall and is exposed to the interior of said mold cavity; and wherein said lining step comprises lining each mold cavity and the exposed portion of said lead wire with a layer of electrically conductive material.
 10. A process according to claim 1; wherein said applying step is carried out while said lined plate is immersed directly in said electrolytic solution without containing thereon any additional means for directing and guiding the metallic ions into said mold cavities. 